1. Field of the Invention
The present invention relates to an image forming apparatus, an image forming method, and a program.
2. Description of the Related Art
Nowadays, in accordance with demands of the market, most electrophotographic apparatuses, such as color copiers and color printers, output color images. Especially, in recent years, because speeds as fast as those of black-and-white output are required during color output, mostly used tandem-type image forming apparatuses include a photosensitive element and a developing device for each color so that a single-color toner image is formed on each photosensitive element and the single-color toner image is sequentially transferred, whereby a color image is recorded on a transfer sheet (for example, see Japanese Patent Application Laid-open No. 2006-126643).
In the tandem-type image forming apparatuses, for both a direct transfer method and an indirect transfer method, an image formed on a photosensitive element for each color is transferred onto a transfer sheet or a belt at a different position from that of other colors on an intermediate transfer belt; therefore, when the moving speed of the intermediate transfer belt is slightly changed, the time to reach the transfer position for a subsequent color is changed, whereby the transfer position for each color is shifted and, as a result, misalignment (color deviation) in the sub-scanning direction may occur on the output image.
A write unit is also separately arranged for each color; therefore, when a magnification in the main scanning direction or a write position is changed due to displacement of a component because of a change in the environment such as a temperature change, misalignment in the main scanning direction may occur on the output image as a result.
Therefore, a tandem-type image forming apparatus performs an alignment control process by forming an alignment control pattern image on an intermediate transfer belt between an image processed area of the preceding page and an image processed area of the following page so as to detect misalignment in the main and sub-scanning directions by using the pattern image and to correct the misalignment.
There is a problem in that the above-described alignment control process requires a certain processing time, which results in the occurrence of downtime during which the process is being executed and a print process cannot be performed, which results in a decrease in printing productivity. Moreover, there is a problem in that, if the black-and-white printing, for which the alignment control is not needed, is interrupted by the alignment control process due to a timer setting, or the like, printing productivity is decreased due to the interruption of the black-and-white printing even though the alignment control is not necessary.
Japanese Patent Application Laid-open No. 2006-126643 discloses a technology in which, when a print job is received before the start of an alignment process, a print process is performed without performing the alignment process and, when a print job is received after the start of the alignment process, the alignment process is interrupted and the print process is started, whereby the priority is put on the print job and a decrease in productivity due to the alignment process is prevented.
However, according to the technology disclosed in Japanese Patent Application Laid-open No. 2006-126643, because the print process cannot be performed during the alignment process, the problem of a decrease in printing productivity has not been resolved.